Organic devices having a fiber structure

ABSTRACT

A photoactive fiber is provided, as well as a method of fabricating such a fiber. The fiber has a conductive core including a first electrode. An organic layer surrounds and is electrically connected to the first electrode. A transparent second electrode surrounds and is electrically connected to the organic layer. Other layers, such as blocking layers or smoothing layers, may also be incorporated into the fiber. The fiber may be woven into a cloth.

This application is a continuation of and claims the benefit of priorityof U.S. patent application Ser. No. 10/892,465, filed on Jul. 16, 2004,which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to organic optoelectronicdevices. More specifically, it is directed to organic optoelectronicdevices having a fiber structure.

BACKGROUND OF THE INVENTION

Optoelectronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodectors. Organic materials may have performanceadvantages over conventional materials. For example, the wavelength atwhich an organic emissive layer emits light (for OLEDs) may generally bereadily tuned with appropriate dopants.

Optoeletronic devices rely on the optical and electronic properties ofmaterials to either produce or detect electromagnetic radiationelectronically or to generate electricity from ambient electromagneticradiation.

Photosensitive optoelectronic devices convert electromagnetic radiationinto electricity. Solar cells, also called photovoltaic (PV) devices,are a type of photosensitive optoelectronic device that is specificallyused to generate electrical power. PV devices, which may generateelectrical energy from light sources other than sunlight, can be used todrive power consuming loads to provide, for example, lighting, heating,or to power electronic circuitry or devices such as calculators, radios,computers or remote monitoring or communications equipment. These powergeneration applications also often involve the charging of batteries orother energy storage devices so that operation may continue when directillumination from the sun or other light sources is not available, or tobalance the power output of the PV device with a specific application'srequirements. As used herein the term “resistive load” refers to anypower consuming or storing circuit, device, equipment or system.

Another type of photosensitive optoelectronic device is a photoconductorcell. In this function, signal detection circuitry monitors theresistance of the device to detect changes due to the absorption oflight.

Another type of photosensitive optoelectronic device is a photodetector.In operation a photodetector is used in conjunction with a currentdetecting circuit which measures the current generated when thephotodetector is exposed to electromagnetic radiation and may have anapplied bias voltage. A detecting circuit as described herein is capableof providing a bias voltage to a photodetector and measuring theelectronic response of the photodetector to electromagnetic radiation.

These three classes of photosensitive optoelectronic devices may becharacterized according to whether a rectifying junction as definedbelow is present and also according to whether the device is operatedwith an external applied voltage, also known as a bias or bias voltage.A photoconductor cell does not have a rectifying junction and isnormally operated with a bias. A PV device has at least one rectifyingjunction and is operated with no bias. A photodetector has at least onerectifying junction and is usually but not always operated with a bias.As a general rule, a photovoltaic cell provides power to a circuit,device or equipment, but does not provide a signal or current to controldetection circuitry, or the output of information from the detectioncircuitry. In contrast, a photodetector or photoconductor provides asignal or current to control detection circuitry, or the output ofinformation from the detection circuitry but does not provide power tothe circuitry, device or equipment.

Traditionally, photosensitive optoelectronic devices have beenconstructed of a number of inorganic semiconductors, e.g., crystalline,polycrystalline and amorphous silicon, gallium arsenide, cadmiumtelluride and others. Herein the term “semiconductor” denotes materialswhich can conduct electricity when charge carriers are induced bythermal or electromagnetic excitation. The term “photoconductive”generally relates to the process in which electromagnetic radiant energyis absorbed and thereby converted to excitation energy of electriccharge carriers so that the carriers can conduct, i.e., transport,electric charge in a material. The terms “photoconductor” and“photoconductive material” are used herein to refer to semiconductormaterials which are chosen for their property of absorbingelectromagnetic radiation to generate electric charge carriers.

PV devices may be characterized by the efficiency with which they canconvert incident solar power to useful electric power. Devices utilizingcrystalline or amorphous silicon dominate commercial applications, andsome have achieved efficiencies of 23% or greater. However, efficientcrystalline-based devices, especially of large surface area, aredifficult and expensive to produce due to the problems inherent inproducing large crystals without significant efficiency-degradingdefects. On the other hand, high efficiency amorphous silicon devicesstill suffer from problems with stability. Present commerciallyavailable amorphous silicon cells have stabilized efficiencies between 4and 8%. More recent efforts have focused on the use of organicphotovoltaic cells to achieve acceptable photovoltaic conversionefficiencies with economical production costs.

PV devices may be optimized for maximum electrical power generationunder standard illumination conditions (i.e., Standard Test Conditionswhich are 1000 W/m², AM1.5 spectral illumination), for the maximumproduct of photocurrent times photovoltage. The power conversionefficiency of such a cell under standard illumination conditions dependson the following three parameters: (1) the current under zero bias,i.e., the short-circuit current I_(SC), (2) the photovoltage under opencircuit conditions, i.e., the open circuit voltage V_(OC), and (3) thefill factor, ff.

PV devices produce a photo-generated current when they are connectedacross a load and are irradiated by light. When irradiated underinfinite load, a PV device generates its maximum possible voltage, Vopen-circuit, or V_(OC). When irradiated with its electrical contactsshorted, a PV device generates its maximum possible current, Ishort-circuit, or I_(SC). When actually used to generate power, a PVdevice is connected to a finite resistive load and the power output isgiven by the product of the current and voltage, I×V. The maximum totalpower generated by a PV device is inherently incapable of exceeding theproduct, I_(SC)×V_(OC). When the load value is optimized for maximumpower extraction, the current and voltage have the values, I_(max) andV_(max), respectively.

A figure of merit for PV devices is the fill factor, ff, defined as:ff={I _(max) V _(max) }/{I _(SC) V _(OC)}  (1)where ff is always less than 1, as I_(SC) and V_(OC) are never obtainedsimultaneously in actual use. Nonetheless, as ff approaches 1, thedevice has less series or internal resistance and thus delivers agreater percentage of the product of I_(SC) and V_(OC) to the load underoptimal conditions. Where P_(inc) is the power incident on a device, thepower efficiency of the device, η_(P), may be calculated by:η_(P) =ff*(I _(SC) *V _(OC))/P_(inc)

When electromagnetic radiation of an appropriate energy is incident upona semiconductive organic material, for example, an organic molecularcrystal (OMC) material, or a polymer, a photon can be absorbed toproduce an excited molecular state. This is represented symbolically asS₀+hν

S₀*. Here S₀ and S₀* denote ground and excited molecular states,respectively. This energy absorption is associated with the promotion ofan electron from a bound state in the HOMO energy level, which may be aπ-bond, to the LUMO energy level, which may be a π*-bond, orequivalently, the promotion of a hole from the LUMO energy level to theHOMO energy level. In organic thin-film photoconductors, the generatedmolecular state is generally believed to be an exciton, i.e., anelectron-hole pair in a bound state which is transported as aquasi-particle. The excitons can have an appreciable life-time beforegeminate recombination, which refers to the process of the originalelectron and hole. recombining with each other, as opposed torecombination with holes or electrons from other pairs. To produce aphotocurrent the electron-hole pair becomes separated, typically at adonor-acceptor interface between two dissimilar contacting organic thinfilms. If the charges do not separate, they can recombine in a geminantrecombination process, also known as quenching, either radiatively, bythe emission of light of a lower energy than the incident light, ornon-radiatively, by the production of heat. Either of these outcomes isundesirable in a photosensitive optoelectronic device.

Electric fields or inhomogeneities at a contact may cause an exciton toquench rather than dissociate at the donor-acceptor interface, resultingin no net contribution to the current. Therefore, it is desirable tokeep photogenerated excitons away from the contacts. This has the effectof limiting the diffusion of excitons to the region near the junction sothat the associated electric field has an increased opportunity toseparate charge carriers liberated by the dissociation of the excitonsnear the junction.

To produce internally generated electric fields which occupy asubstantial volume, the usual method is to juxtapose two layers ofmaterial with appropriately selected conductive properties, especiallywith respect to their distribution of molecular quantum energy states.The interface of these two materials is called a photovoltaicheterojunction. In traditional semiconductor theory, materials forforming PV heterojunctions have been denoted as generally being ofeither n or p type. Here n-type denotes that the majority carrier typeis the electron. This could be viewed as the material having manyelectrons in relatively free energy states. The p-type denotes that themajority carrier type is the hole. Such material has many holes inrelatively free energy states. The type of the background, i.e., notphoto-generated, majority carrier concentration depends primarily onunintentional doping by defects or impurities. The type andconcentration of impurities determine the value of the Fermi energy, orlevel, within the gap between the highest occupied molecular orbital(HOMO) energy level and the lowest unoccupied molecular orbital (LUMO)energy level, called the HOMO-LUMO gap. The Fermi energy characterizesthe statistical occupation of molecular quantum energy states denoted bythe value of energy for which the probability of occupation is equal to½. A Fermi energy near the LUMO energy level indicates that electronsare the predominant carrier. A Fermi energy near the HOMO energy levelindicates that holes are the predominant carrier. Accordingly, the Fermienergy is a primary characterizing property of traditionalsemiconductors and the prototypical PV heterojunction has traditionallybeen the p-n interface.

The term “rectifying” denotes, inter alia, that an interface has anasymmetric conduction characteristic, i.e., the interface supportselectronic charge transport preferably in one direction. Rectificationis associated normally with a built-in electric field which occurs atthe heterojunction between appropriately selected materials.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

In the context of organic materials, the terms “donor” and “acceptor”refer to the relative positions of the HOMO and LUMO energy levels oftwo contacting but different organic materials. This is in contrast tothe use of these terms in the inorganic context, where “donor” and“acceptor” may refer to types of dopants that may be used to createinorganic n- and p-types layers, respectively. In the organic context,if the LUMO energy level of one material in contact with another islower, then that material is an acceptor. Otherwise it is a donor. It isenergetically favorable, in the absence of an external bias, forelectrons at a donor-acceptor junction to move into the acceptormaterial, and for holes to move into the donor material.

A significant property in organic semiconductors is carrier mobility.Mobility measures the ease with which a charge carrier can move througha conducting material in response to an electric field. In the contextof organic photosensitive devices, a layer including a material thatconducts preferentially by electrons due to a high electron mobility maybe referred to as an electron transport layer, or ETL. A layer includinga material that conducts preferentially by holes due to a high holemobility may be referred to as a hole transport layer, or HTL.Preferably, but not necessarily, an acceptor material is an ETL and adonor material is a HTL.

Conventional inorganic semiconductor PV cells employ a p-n junction toestablish an internal field. Early organic thin film cells, such asreported by Tang et al, Appl. Phys Lett. 48, 183 (1986), contain aheterojunction analogous to that employed in a conventional inorganic PVcell. However, it is now recognized that in addition to theestablishment of a p-n type junction, the energy level offset of theheterojunction also plays an important role.

The energy level offset at the organic D-A heterojunction is believed tobe important to the operation of organic PV devices due to thefundamental nature of the photogeneration process in organic materials.Upon optical excitation of an organic material, localized Frenkel orcharge-transfer excitons are generated. For electrical detection orcurrent generation to occur, the bound excitons must be dissociated intotheir constituent electrons and holes. Such a process can be induced bythe built-in electric field, but the efficiency at the electric fieldstypically found in organic devices (F˜10⁶ V/cm) is low. The mostefficient exciton dissociation in organic materials occurs at adonor-acceptor (D-A) interface. At such an interface, the donor materialwith a low ionization potential forms a heterojunction with an acceptormaterial with a high electron affinity. Depending on the alignment ofthe energy levels of the donor and acceptor materials, the dissociationof the exciton can become energetically favorable at such an interface,leading to a free electron polaron in the acceptor material and a freehole polaron in the donor material.

Organic PV cells have many potential advantages when compared totraditional silicon-based devices. Organic PV cells are light weight,economical in materials use, and can be deposited on low costsubstrates, such as flexible plastic foils. However, some organic PVdevices typically have relatively low external quantum efficiency, beingon the order of 1% or less. This is, in part, thought to be due to thesecond order nature of the intrinsic photoconductive process. That is,carrier generation requires exciton generation, diffusion and ionizationor collection. There is an efficiency η associated with each of theseprocesses. Subscripts may be used as follows: P for power efficiency,EXT for external quantum efficiency, A for photon absorption, ED fordiffusion, CC for collection, and INT for internal quantum efficiency.Using this notation:η_(P)˜η_(NEXT)=η_(A)*η_(ED)*η_(cc)η_(EXT)=η_(A)*η_(INT)

The diffusion length (L_(D)) of an exciton is typically much less(L_(D)˜50 Å) than the optical absorption length (˜500 Å), requiring atrade off between using a thick, and therefore resistive, cell withmultiple or highly folded interfaces, or a thin cell with a low opticalabsorption efficiency.

Typically, when light is absorbed to form an exciton in an organic thinfilm, a singlet exciton is formed. By the mechanism of intersystemcrossing, the singlet exciton may decay to a triplet exciton. In thisprocess energy is lost which will result in a lower efficiency for thedevice. If not for the energy loss from intersystem crossing, it wouldbe desirable to use materials that generate triplet excitons, as tripletexcitons generally have a longer lifetime, and therefore a longerdiffusion length, than do singlet excitons.

SUMMARY OF THE INVENTION

A photoactive fiber is provided, as well as a method of fabricating sucha fiber. The fiber has a conductive core including a first electrode. Anorganic layer surrounds and is electrically connected to the firstelectrode. A transparent second electrode surrounds and is electricallyconnected to the organic layer. Other layers, such as blocking layers orsmoothing layers, may also be incorporated into the fiber. The fiber maybe woven into a cloth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic PV device comprising an anode, an anodesmoothing layer, a donor layer, an acceptor layer, a blocking layer, anda cathode.

FIG. 2 shows a photoactive fiber.

FIG. 3 shows a photoactive fiber including a blocking layer.

FIG. 4 shows an organic light emitting device.

DETAILED DESCRIPTION

An organic optoelectronic device is provided, having a fiber structure.Various types of organic optoelectronic devices may be provided,including organic photosensitive devices and organic light emittingdevices. Embodiments of the present invention may comprise an anode, acathode, and an organic layer disposed between and electricallyconnected to the anode and the cathode.

Organic photosensitive devices of embodiments of the present inventionmay be used, for example, to generate a usable electrical current fromincident electromagnetic radiation (e.g., PV devices) or may be used todetect incident electromagnetic radiation. A “photoactive region” is theportion of the photosensitive device that absorbs electromagneticradiation to generate excitons that may dissociate in order to generatean electrical current. Organic photosensitive optoelectronic devices mayinclude at least one transparent electrode to allow incident radiationto be absorbed by the device. Several PV device materials andconfigurations are described in U.S. Pat. Nos. 6,657,378, 6,580,027, and6,352,777, which are incorporated herein by reference in their entirety.

FIG. 1 shows an organic photosensitive optoelectronic device 100. Thefigures are not necessarily drawn to scale. Device 100 may include asubstrate 110, an anode 115, an anode smoothing layer 120, a donor layer125, an acceptor layer 130, a blocking layer 135, and a cathode 140.Cathode 140 may be a compound cathode having a first conductive layerand a second conductive layer. Device 100 may be fabricated bydepositing the layers described, in order. Charge separation may occurpredominantly at the organic heterojunction between donor layer 125 andacceptor layer 130. The built-in potential at the heterojunction isdetermined by the HOMO-LUMO energy level difference between the twomaterials contacting to form the heterojunction. The HOMO-LUMO gapoffset between the donor and acceptor materials produce an electricfield at the donor/acceptor interface that facilitates charge separationfor excitons created within an exciton diffusion length of theinterface.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

FIG. 4 shows an organic light emitting device 400. The figures are notnecessarily drawn to scale. Device 400 may include a substrate 410, ananode 415, a hole injection layer 420, a hole transport layer 425, anelectron blocking layer 430, an emissive layer 435, a hole blockinglayer 440, an electron transport layer 445, an electron injection layer450, a protective layer 455, and a cathode 460. Cathode 460 is acompound cathode having a first conductive layer 462 and a secondconductive layer 464. Device 400 may be fabricated by depositing thelayers described, in order.

The specific composition and arrangement of layers illustrated in FIGS.1 and 4 is exemplary only, and is not intended to be limiting. Forexample, some of the layers (such as blocking layers) may be omitted.Other layers (such as reflective layers and/or antireflective layers)may be added. For photosensitive devices, additional acceptor and donorlayers may be used (i.e., tandem cells), or other types of organicphotosensitive devices may be used that do not have separate organicacceptor and donor layers. Other types of OLEDs may be used, such asOLEDs without electron and/or hole transport layers. The order of layersmay be altered. Arrangements other than those specifically describedherein may be used. One of skill in the art, with the benefit of thisdisclosure, should be able to adapt various organic deviceconfigurations to a fiber structure.

The specific materials and structures described are exemplary in nature,and other materials and structures may be used. Functional devices maybe achieved by combining the various layers described in different ways,or layers may be omitted entirely, based on design, performance, andcost factors. Other layers not specifically described may also beincluded. Materials other than those specifically described may be used.Although many of the examples provided herein describe various layers ascomprising a single material, it is understood that combinations ofmaterials, such as a mixture of host and dopant, or more generally amixture, may be used. Also, the layers may have various sublayers. Thenames given to the various layers herein are not intended to be strictlylimiting. For example, in an OLED, an electron blocking layer may alsofunction as a hole transport layer. In one embodiment, an OLED orphotosensitive device may be described as having an “organic layer”disposed between a cathode and an anode. This organic layer may comprisea single layer, or may further comprise multiple layers of differentorganic materials as described, for example, with respect to FIGS. 1 and2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190, Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The device structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 4.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

The substrate may be any suitable substrate that provides desiredstructural properties. The substrate may be flexible or rigid. Thesubstrate may be transparent, translucent or opaque. Plastic and glassare examples of preferred rigid substrate materials. Plastic and metalfoils are examples of preferred flexible substrate materials. Thematerial and thickness of the substrate may be chosen to obtain desiredstructural and optical properties.

U.S. Pat. No. 6,352,777, incorporated herein by reference, providesexamples of electrodes, or contacts, that may be used in anoptoelectronic device. When used herein, the terms “electrode” and“contact” refer to layers that provide a medium for deliveringphoto-generated current to an external circuit or providing a biasvoltage to the device. An electrode, or contact, provides the interfacebetween the photoactive regions of an organic photosensitiveoptoelectronic device and a wire, lead, trace or other means fortransporting the charge carriers to or from the external circuit. In aphotosensitive optoelectronic device, it is desirable to allow themaximum amount of ambient electromagnetic radiation from the deviceexterior to be admitted to the photoconductively active interior region.Electromagnetic radiation reaches a photoconductive layer(s) may beconverted to electricity by photoconductive absorption. This oftendictates that at least one of the electrical contacts should beminimally absorbing and minimally reflecting of the incidentelectromagnetic radiation. Preferably, such a contact is substantiallytransparent. The opposing electrode may be a reflective material so thatlight which has passed through the cell without being absorbed isreflected back through the cell. As used herein, a layer of material ora sequence of several layers of different materials is said to be“transparent” when the layer or layers permit at least 50% of theambient electromagnetic radiation in relevant wavelengths to betransmitted through the layer or layers. Similarly, layers which permitsome, but less that 50% transmission of ambient electromagneticradiation in relevant wavelengths are said to be “semi-transparent.”

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. For example, for a devicehaving two electrodes, the bottom electrode is the electrode closest tothe substrate, and is generally the first electrode fabricated. Thebottom electrode has two surfaces, a bottom surface closest to thesubstrate, and a top surface further away from the substrate. Where afirst layer is described as “disposed over” a second layer, the firstlayer is disposed further away from substrate. There may be other layersbetween the first and second layer, unless it is specified that thefirst layer is “in physical contact with” the second layer. For example,a cathode may be described as “disposed over” an anode, even thoughthere are various organic layers in between. In the context of a coaxialdevice or other non-planar configuration, “disposed over” means disposedfurther from the part of the structure that serves as a core orsubstrate, i. e., the part of the structure over which the rest of thestructure is fabricated.

The electrodes are preferably composed of metals or “metal substitutes”.Herein the term “metal” is used to embrace both materials composed of anelementally pure metal, e.g., Mg, and also metal alloys which arematerials composed of two or more elementally pure metals, e.g., Mg andAg together, denoted Mg:Ag. Here, the term “metal substitute” refers toa material that is not a metal within the normal definition, but whichhas the metal-like properties that are desired in certain appropriateapplications. Commonly used metal substitutes for electrodes and chargetransfer layers would include doped wide-bandgap semiconductors, forexample, transparent conducting oxides such as indium tin oxide (ITO),gallium indium tin oxide (GITO), and zinc indium tin oxide (ZITO). Inparticular, ITO is a highly doped degenerate n+ semiconductor with anoptical bandgap of approximately 3.2 eV, rendering it transparent towavelengths greater than approximately 3900 Å. Another suitable metalsubstitute is the transparent conductive polymer polyanaline (PANI) andits chemical relatives. Metal substitutes may be further selected from awide range of non-metallic materials, wherein the term “non-metallic” ismeant to embrace a wide range of materials provided that the material isfree of metal in its chemically uncombined form. When a metal is presentin its chemically uncombined form, either alone or in combination withone or more other metals as an alloy, the metal may alternatively bereferred to as being present in its metallic form or as being a “freemetal”. Thus, the metal substitute electrodes of the present inventionmay sometimes be referred to as “metal-free” wherein the term“metal-free” is expressly meant to embrace a material free of metal inits chemically uncombined form. Free metals typically have a form ofmetallic bonding that results from a sea of valence electrons which arefree to move in an electronic conduction band throughout the metallattice. While metal substitutes may contain metal constituents they are“non-metallic” on several bases. They are not pure free-metals nor arethey alloys of free-metals. When metals are present in their metallicform, the electronic conduction band tends to provide, among othermetallic properties, a high electrical conductivity as well as a highreflectivity for optical radiation.

Embodiments of the present invention may include, as one or more of thetransparent electrodes of an optoelectronic device, a highlytransparent, non-metallic, low resistance cathode such as disclosed inU.S. Pat. No. 6,420,031, to Parthasarathy et al. (“Parthasarathy '031”),or a highly efficient, low resistance metallic/non-metallic compoundcathode such as disclosed in U.S. Pat. No. 5,703,436 to Forrest et al.(“Forrest '436”), both incorporated herein by reference in theirentirety. Each type of cathode is preferably prepared in a fabricationprocess that includes the step of sputter depositing an ITO layer ontoeither an organic material, such as copper phthalocyanine (CuPc), toform a highly transparent, non-metallic, low resistance cathode or ontoa thin Mg:Ag layer to form a highly efficient, low resistancemetallic/non-metallic compound cathode.

Herein, the term “cathode” is used in the following manner. In anon-stacked PV device or a single unit of a stacked PV device underambient irradiation and connected with a resistive load and with noexternally applied voltage, e.g., a PV device, electrons move to thecathode from the photo-conducting material. In an OLED, electrons areinjected into the device from the cathode. Similarly, the term “anode”is used herein such that in a PV device under illumination, holes moveto the anode from the photo-conducting material, which is equivalent toelectrons moving in the opposite manner. Holes It will be noted that asthe terms are used herein, anodes and cathodes may be electrodes orcharge transfer layers.

An organic photosensitive device will comprise at least one photoactiveregion in which light is absorbed to form an excited state, or“exciton”, which may subsequently dissociate in to an electron and ahole. The dissociation of the exciton will typically occur at theheterojunction formed by the juxtaposition of an acceptor layer and adonor layer. For example, in the device of FIG. 1, the “photoactiveregion” may include donor layer 125 and acceptor layer 130.

The acceptor material may be comprised of, for example, perylenes,naphthalenes, fullerenes or nanotubules. An example of an acceptormaterial is 3,4,9,10-perylenetetracarboxylic bis-benzimidazole (PTCBI).Alternatively, the acceptor layer may be comprised of a fullerenematerial as described in U.S. Pat. No. 6,580,027, incorporated herein byreference in its entirety. Adjacent to the acceptor layer, is a layer oforganic donor-type material. The boundary of the acceptor layer and thedonor layer forms the heterojunction which may produce an internallygenerated electric field. The material for the donor layer may be apthalocyanine or a porphyrin, or a derivative or transition metalcomplex thereof, such as copper pthalocyanine (CuPc). Other suitableacceptor and donor materials may be used.

Through the use of an organometallic material in the photoactive region,photosensitive devices incorporating such materials may efficientlyutilize triplet excitons. It is believed that the singlet-triplet mixingmay be so strong for organometallic compounds, that the absorptionsinvolve excitation from the singlet ground states directly to thetriplet excited states, eliminating the losses associated withconversion from the singlet excited state to the triplet excited state.The longer lifetime and diffusion length of triplet excitons incomparison to singlet excitons may allow for the use of a thickerphotoactive region, as the triplet excitons may diffuse a greaterdistance to reach the donor-acceptor heterojunction, without sacrificingdevice efficiency. Materials other than organometallics may also beused.

In a preferred embodiment of the invention, the stacked organic layersof a photosensitive device include one or more exciton blocking layers(EBLs) as described in U.S. Pat. No. 6,097,147, Peumans et al, AppliedPhysics Letters 2000, 76, 2650-52, and co-pending application Ser. No.09/449,801, filed Nov. 26, 1999, both incorporated herein by reference.In PV devices, higher internal and external quantum efficiencies havebeen achieved by the inclusion of an EBL to confine photogeneratedexcitons to the region near the dissociating interface and to preventparasitic exciton quenching at a photosensitive organic/electrodeinterface. In addition to limiting the volume over which excitons maydiffuse, an EBL can also act as a diffusion barrier to substancesintroduced during deposition of the electrodes. In some circumstances,an EBL can be made thick enough to fill pinholes or shorting defectswhich could otherwise render an organic PV device non-functional. An EBLcan therefore help protect fragile organic layers from damage producedwhen electrodes are deposited onto the organic materials.

It is believed that the EBLs derive their exciton blocking property fromhaving a LUMO-HOMO energy gap substantially larger than that of theadjacent organic semiconductor from which excitons are being blocked.Thus, the confined excitons are prohibited from existing in the EBL dueto energy considerations. While it is desirable for the EBL to blockexcitons, it is not desirable for the EBL to block all charge. However,due to the nature of the adjacent energy levels, an EBL may block onesign of charge carrier. By design, an EBL will exist between two otherlayers, usually an organic photosensitive semiconductor layer and aelectrode or charge transfer layer. The adjacent electrode or chargetransfer layer will be in context either a cathode or an anode.Therefore, the material for an EBL in a given position in a device willbe chosen so that the desired sign of carrier will not be impeded in itstransport to the electrode or charge transfer layer. Proper energy levelalignment ensures that no barrier to charge transport exists, preventingan increase in series resistance. For example, it is desirable for amaterial used as a cathode side EBL to have a LUMO energy level closelymatching the LUMO energy level of the adjacent ETL material so that anyundesired barrier to electrons is minimized.

It should be appreciated that the exciton blocking nature of a materialis not an intrinsic property of its HOMO-LUMO energy gap. Whether agiven material will act as an exciton blocker depends upon the relativeHOMO and LUMO energy levels of the adjacent organic photosensitivematerial. Therefore, it is not possible to identify a class of compoundsin isolation as exciton blockers without regard to the device context inwhich they may be used. However, with the teachings herein one ofordinary skill in the art may identify whether a given material willfunction as an exciton blocking layer when used with a selected set ofmaterials to construct an organic PV device.

In a preferred embodiment of the invention, an EBL is situated betweenthe acceptor layer and the cathode of a photosensitive device. Apreferred material for the EBL comprises2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (also called bathocuproineor BCP), which is believed to have a LUMO-HOMO energy level separationof about 3.5 eV, orbis(2-methyl-8-hydroxyquinolinoato)-aluminum(III)phenolate (Alq₂OPH).BCP is an effective exciton blocker which can easily transport electronsto the cathode from an acceptor layer.

The EBL layer may be doped with a suitable dopant, including but notlimited to 3,4,9,10-perylenetracarboxylic dianhydride (PTCDA),3,4,9,10-perylenetracarboxylic diimide (PTCDI),3,4,9,10-perylenetetracarboxylic-bis-benzimidazole (PTCBI),1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), and derivativesthereof. It is thought that the BCP as deposited in the present devicesis amorphous. The present apparently amorphous BCP exciton blockinglayers may exhibit film recrystallization, which is especially rapidunder high light intensities. The resulting morphology change topolycrystalline material results in a lower quality film with possibledefects such as shorts, voids or intrusion of electrode material.Accordingly, it has been found that doping of some EBL materials, suchas BCP, that exhibit this effect with a suitable, relatively large andstable molecule can stabilize the EBL structure to prevent performancedegrading morphology changes. It should be further appreciated thatdoping of an EBL which is transporting electrons in a giving device witha material having a LUMO energy level close to that of the EBL will helpinsure that electron traps are not formed which might produce spacecharge build-up and reduce performance. Additionally, it should beappreciated that relatively low doping densities should minimize excitongeneration at isolated dopant sites. Since such excitons are effectivelyprohibited from diffusing by the surrounding EBL material, suchabsorptions reduce device photoconversion efficiency.

Representative embodiments of photoactive devices may also comprisetransparent charge transfer layers or charge recombination layers. Asdescribed herein charge transfer layers are distinguished from acceptorand donor layers by the fact that charge transfer layers are frequently,but not necessarily, inorganic (often metals) and they may be chosen notto be photoconductively active. The term “charge transfer layer” is usedherein to refer to layers similar to but different from electrodes inthat a charge transfer layer only delivers charge carriers from onesubsection of an optoelectronic device to the adjacent subsection. Theterm “charge recombination layer” is used herein to refer to layerssimilar to but different from electrodes in that a charge recombinationlayer allows for the recombination of electrons and holes between tandemphotosensitive devices and may also enhance internal optical fieldstrength near one or more photoactive layers. A charge recombinationlayer can be constructed of semi-transparent metal nanoclusters,nanoparticle or nanorods as described in U.S. Pat. No. 6,657,378,incorporated herein by reference in its entirety.

In a preferred embodiment of the invention, an anode-smoothing layer issituated between the anode and the donor layer. A preferred material forthis layer comprises a film of3,4-polyethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS). Theintroduction of the PEDOT:PSS layer between the anode (ITO) and thedonor layer (CuPc) may lead to greatly improved fabrication yields. Thisis attributed to the ability of the spin-coated PEDOT:PSS film toplanarize the ITO, whose rough surface could otherwise result in shortsthrough the thin molecular layers.

In a further embodiment on the invention, one or more of the layers maybe treated with plasma prior to depositing the next layer. The layersmay be treated, for example, with a mild argon or oxygen plasma. Thistreatment is beneficial as it reduces the series resistance. It isparticularly advantageous that the PEDOT:PSS layer be subject to a mildplasma treatment prior to deposition of the next layer.

The simple layered structure illustrated in FIG. 1 is provided by way ofnon-limiting example, and it is understood that embodiments of theinvention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional devices may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. Organic layers that are not a partof the photoactive region, i.e., organic layers that generally do notabsorb photons that make a significant contribution to photocurrent, maybe referred to as “non-photoactive layers.” Examples of non-photoactivelayers include EBLs and anode-smoothing layers. Other types ofnon-photoactive layers may also be used.

Preferred organic materials for use in the photoactive layers of aphotosensitive device include cyclometallated organometallic compounds.The term “organometallic” as used herein is as generally understood byone of ordinary skill in the art and as given, for example, in“Inorganic Chemistry” (2nd Edition) by Gary L. Miessler and Donald A.Tarr, Prentice Hall (1998). Thus, the term organometallic refers tocompounds which have an organic group bonded to a metal through acarbon-metal bond. This class does not include per se coordinationcompounds, which are substances having only donor bonds fromheteroatoms, such as metal complexes of amines, halides, pseudohalides(CN, etc.), and the like. In practice organometallic compounds generallycomprise, in addition to one or more carbon-metal bonds to an organicspecies, one or more donor bonds from a heteroatom. The carbon-metalbond to an organic species refers to a direct bond between a metal and acarbon atom of an organic group, such as phenyl, alkyl, alkenyl, etc.,but does not refer to a metal bond to an “inorganic carbon,” such as thecarbon of CN or CO. The term cyclometallated refers to compounds thatcomprise an bidentate organometallic ligand so that, upon bonding to ametal, a ring structure is formed that includes the metal as one of thering members.

Organic layers may be fabricated using vacuum deposition, spin coating,organic vapor-phase deposition, inkjet printing and other methods knownin the art.

Organic photosensitive optoelectronic devices of embodiments of thepresent invention may function as a PV, photodetector or photoconductor.Whenever the organic photosensitive optoelectronic devices of thepresent invention function as a PV device, the materials used in thephotoconductive organic layers and the thicknesses thereof may beselected, for example, to optimize the external quantum efficiency ofthe device. Whenever the organic photosensitive optoelectronic devicesof the present invention function as photodetectors or photoconductors,the materials used in the photoconductive organic layers and thethicknesses thereof may be selected, for example, to maximize thesensitivity of the device to desired spectral regions.

This result may be achieved by considering several guidelines that maybe used in the selection of layer thicknesses. It is desirable for theexciton diffusion length, L_(D), to be greater than or comparable to thelayer thickness, L, since it is believed that most exciton dissociationwill occur at an interface. If L_(D) is less than L, then many excitonsmay recombine before dissociation. It is further desirable for the totalphotoconductive layer thickness to be of the order of theelectromagnetic radiation absorption length, 1/α (where α is theabsorption coefficient), so that nearly all of the radiation incident onthe PV device is absorbed to produce excitons. Furthermore, thephotoconductive layer thickness should be as thin as possible to avoidexcess series resistance due to the high bulk resistivity of organicsemiconductors.

Accordingly, these competing guidelines inherently require tradeoffs tobe made in selecting the thickness of the photoconductive organic layersof a photosensitive optoelectronic cell. Thus, on the one hand, athickness that is comparable or larger than the absorption length isdesirable (for a single cell device) in order to absorb the maximumamount of incident radiation. On the other hand, as the photoconductivelayer thickness increases, two undesirable effects are increased. One isthat due to the high series resistance of organic semiconductors, anincreased organic layer thickness increases device resistance andreduces efficiency. Another undesirable effect is that increasing thephotoconductive layer thickness increases the likelihood that excitonswill be generated far from the effective field at a charge-separatinginterface, resulting in enhanced probability of geminate recombinationand, again, reduced efficiency. Therefore, a device configuration isdesirable which balances between these competing effects in a mannerthat produces a high external quantum efficiency for the overall device.

Organic photosensitive optoelectronic devices of may function asphotodetectors. In this embodiment, the device may be a multilayerorganic device, for example as described in U.S. application Ser. No.10/723,953, filed Nov. 26, 2003, incorporated herein by reference in itsentirety. In this case an external electric field may be generallyapplied to facilitate extraction of the separated charges.

A concentrator or trapping configuration can be employed to increase theefficiency of the organic photosensitive optoelectronic device, wherephotons are forced to make multiple passes through the thin absorbingregions. U.S. Pat. Nos. 6,333,458 and 6,440,769, incorporated herein byreference in their entirety, addresses this issue by using structuraldesigns that enhance the photoconversion efficiency of photosensitiveoptoelectronic devices by optimizing the optical geometry for highabsorption and for use with optical concentrators that increasecollection efficiency. Such geometries for photosensitive devicessubstantially increase the optical path through the material by trappingthe incident radiation within a reflective cavity or waveguidingstructure, and thereby recycling light by multiple reflection throughthe photoresponsive material. The geometries disclosed in U.S. Pat. Nos.6,333,458 and 6,440,769 therefore enhance the external quantumefficiency of the devices without causing substantial increase in bulkresistance. Included in the geometry of such devices is a firstreflective layer; a transparent insulating layer which should be longerthan the optical coherence length of the incident light in alldimensions to prevent optical microcavity interference effects; atransparent first electrode layer adjacent the transparent insulatinglayer; a photosensitive heterostructure adjacent the transparentelectrode; and a second electrode which is also reflective.

Coatings may be used to focus optical energy into desired regions of adevice. U.S. patent application Ser. No. 10/857,747, which isincorporated by reference in its entirety, provides examples of such acoating.

Organic solar cells typically consist of thin (about 100 nm) layers ofmolecular or polymeric organic compounds sandwiched between metal andITO electrodes. The ITO may be sputtered onto glass or plastic sheets,the organic materials may be deposited by vacuum thermal evaporation(VTE), vapor phase deposition (OVPD), spin-casting or dip-coating. Metalcathodes may be thermally evaporated in vacuum. The device may beilluminated from the ITO side. Unlike the silicon photovoltaic cell,photon absorption may not immediately generate charge pairs.Photocurrent generation in this structure may occur in four consecutivesteps: 1) photon absorption to generate a bound charge pair, known asthe Frenkel exciton, 2) exciton diffusion to the donor-acceptorinterface, 3) exciton dissociation into an electron-hole pair, and 4)collection of the electrons and holes at the electrodes. Generally, thedonor material is chosen to have a low ionization potential (IP), whilethe acceptor material has a high electron affinity (EA), driving theexothermic dissociation of the exciton at the interface.

The individual layers may preferably be sufficiently thick for efficientabsorption of light, while being within the characteristic diffusionlength of the excitons. Table 1, below, provides a list of typicalexciton diffusion lengths for some preferred organic PV cell materials.Material L_(D) (Å) Technique Reference Small Molecule Systems PTCBI 30 ±3 PL quenching (1) PTCDA 880 ± 60 from η_(EQE) (3) PPEI ˜700 PLquenching (5) CuPc 100 ± 30 from η_(EQE) (1) 680 ± 200 from η_(EQE) (6)ZnPc 300 ± 100 from η_(EQE) (7) C₆₀ 400 ± 50 from η_(EQE) (1) 141 fromη_(EQE) (2) Alq₃ 200 (8) ˜200 (9) Polymer Systems PPV 70 ± 10 fromη_(EQE) (4) 120 ± 30 from η_(EQE) (6) PEOPT 47 from η_(EQE) (2) 50 PLquenching (10) 

In the above table, PPEI is perylene bis(phenethylimide), alq₃ istris(8-hydroxyquinoline)aluminum, CuPc is copper phthalocyanine, ZnPc iszinc phthalocyanine. The result for PPEI is calculated using the resultfor a SnO² quenching surface and assuming infinite surface recombinationvelocity. The results leading to L_(D) for PPEI of 2.5±0.5 μm are likelyinfluenced by quencher diffusion and morphological changes duringsolvent vapor assisted annealing. The result for PPV with 120±30 doesnot take into consideration optical interference effects. The diffusionlength measurements were obtained from the following sources: (1)Peumans, P.; Yakimov, A.; Forrest, S. R., J. Appl. Phys. 2003, 93, 3693;(2) L. A. A. Pettersson et al., J. Appl. Phys., 86, 487 (1999); (3) V.Bulovic and S. R. Forrest, Chem. Phys. 210, 13 (1996); (4) J. J. M.Halls et al., Appl. Phys. Lett. 68, 3120 (1996); (5) B. A. Gregg et al.,J. Phys. Chem. B 101, 5362 (1997); (6) T. Stübinger and W. Brütting, J.Appl. Phys. 90, 3632 (2001); (7) H. R. Kerp and E. E. van Faassen, Nord.Hydrol. 1, 1761 (1999); (8) A. L. Burin and M. A. Ratner, J. Phys. Chem.A 104, 4704 (2000); (9) V. E. Choong et al., J. Vac. Sci. Technol. A 16,1838 (1998); (10) M Theander, et al., Phys. Rev. B 61, 12957 (2000).

Because of high absorption coefficients in many organic compounds (e.g.,copper phthalocyanine), on balance this leads to desirable layerthicknesses of 100 to 1000 Å—much thinner than the active layers insilicon-based or Gratzel photovoltaic cells. The organic molecules andpolymer chains may be held together by van der Waals forces, and mayform low-density (1.1 g/cm³) solid films at ambient conditions. Thefilms can be deposited at low substrate temperatures, allowing organicphotovoltaic cells to be built on a variety of substrates, without needto lattice match the active layers to the substrate, and at a modestthermal budget.

Tang and Van Slyke demonstrated an organic heterojunction photovoltaiccell in 1986, having a quantum efficiency of 1%. Primarily, however,this first heterojunction photovoltaic cell was limited because of theshort diffusion length of excitons, which caused most of the generatedexcitons to decay (into phonons) before reaching the interface. Progressin flat heterojunction organic photovoltaic cells has been slow, untilrecently, when materials such as C₆₀ having long exciton diffusionlengths were introduced, as well as novel device structures, such as thebulk heterojunction.

The bulk heterojunction may be an interpenetrating network of donor andacceptor materials. Unlike a substantially flat heterojunction, theabsorption of a photon may occur near the donor-acceptor interface,increasing the probability of charge dissociation. To fabricate the bulkheterojunction, a mixed donor-acceptor molecular film may be depositedon a substrate and annealed, to induce phase-separation. Similarly, twopolymers may be spin-cast and allowed to phase-segregate, producing aninterpenetrating structure. Efficiencies as high as 3.5% have beenachieved in both polymer and small molecule systems.

General information regarding C₆₀ and efficiencies may be available at,for example, Peumans, P. and S. R. Forrest, Very-High-EfficiencyDouble-Heterostructure Copper Phthalocyanine/C60 Photovoltaic Cells,Applied Physics Letters, 2001, 79(1): p. 126. General informationregarding bulk heterojunction (bulk heterojunction) structures may befound at Peumans, P., S. Uchida, and S. R. Forrest, Efficient BulkHeterojunction Photovoltaic Cells Using Small-Molecular-Weight OrganicThin Films, Nature, 2003, 425(6954): p. 158 and/or Shaheen, S. E., etal., 2.5% Efficient Organic Plastic Solar Cells, Applied PhysicsLetters, 2001, 78(6): p. 841.

Greater gains may be anticipated by using better organic materials,tandem photovoltaic cells, and metallic nanoclusters. The preceding listis exemplary and is not intended to be exclusive. General informationregarding metallic nanoclusters may be found in Yakimov, A. and S. R.Forrest, High Photovoltage Multiple-Heterojunction Organic Solar CellsIncorporating Interfacial Metallic Nanoclusters. Applied PhysicsLetters, 2002, 80(9) p. 1667-1669.

While known organic photovoltaic cells may not be more efficient thansilicon or Gratzel cells, they are potentially easier and less expensiveto produce. Organic materials also allow a broader choice of substrates.Disclosed in one embodiment herein is a method of fabrication of anorganic photovoltaic cell (in fiber form) that, with the present stateof the art and materials, should result in 3.5% or greater efficientsolar cells, but at a significantly reduced cost and in a more versatileform factor than in comparison with known organic photovoltaic cells.

FIG. 2 shows a representation of a photoactive fiber structure 200 inaccordance with an embodiment of the invention. For clarity ofillustration, FIG. 2 may not be to scale. The photoactive fiberstructure 200 may comprise a support element 202; a first electrode 204,which may substantially surround the support element 202; an organiclayer 206, which may substantially surround the first electrode layer204 and which comprises a photoactive region; a second electrode 208,which may substantially surround the organic layer 206; and a auxiliaryconductor 210, which may be in electrical contact with some surface ofthe transparent electrode 208. The photoactive fiber structure 200 inaccordance with an embodiment of the invention may further comprise anouter layer 212.

In one embodiment, support element 202 may be fabricated of a flexiblesolid material. Examples may include an optical fiber, atelecommunications fiber, and a solid nylon strand. In one embodiment,the core may be a solid nylon strand. Other materials are acceptablewithout departing from the scope of the invention, and a wide variety ofdimensions may be used depending upon the structural requirements of aparticular application. Together, support element 202 and firstelectrode 204 comprise a “conductive core.” Support element 202 may beconductive or non-conductive. In one embodiment, the conductive core maybe a single element, without the need for a support element 202 separatefrom first electrode 204. Preferable, such a conductive core comprises amaterial that provides sufficient structural properties andconductivity. Metal wires are a preferred example of such a conductivecore. Whether or not there is a separate support element 202, firstelectrode 204 may be comprised of two or more layers (such as, forexample, a first layer of aluminum surrounded by a second layer oflithium). Examples of suitable conductive materials include silver,gold, copper, and aluminum. Other conductive materials may be used.Preferably, the conductive core is flexible.

In one embodiment, organic layer 206 may be a polymer or small-molecularbulk heterojunction coating. In one embodiment, the organic layer 206may range in thickness from about 1 to 200 nm. Examples of polymer orsmall-molecular bulk heterojunction coatings include PCBM-nMDMO-PPV andCuPc-C₆₀, respectively. As used herein,

-   PCBM is 6,6-phenyl-C61-Butyl acid-methylester-   MDMO-PPV is    poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene-vinylene)-   PPV is poly(1,4-phenylene-vinylene)-   C₆₀ is buckminsterfullerene-   PtOEP is 2,3,7,8,12,13,17,18-Octaethyl-21H,23H-porphine    platinum (II) (also platinum octaethylporphyrin)-   PTCBI is 3,4,9,10-perylenetetracarboxylic bis-benzimidazole    Other organic layers, such as a planar heterojunction layer or a    mixed heterojunction layer, as well as other material combinations,    that provide photogeneration may also be selected without departing    from the scope of the invention.

In one embodiment, second electrode 208 may be transparent and comprisea polymer comprised of PEDOT-PSS. ITO is another preferred material.Preferably, second electrode 208 is transparent and flexible. Othertransparent electrode materials, whether metallic or non-metallic, mayalso be selected without departing from the scope of the invention.

In one embodiment, the outer layer 212 may be an optically transparentnylon. Other materials may also be used. Depending upon the amount ofprotection from the environment that is needed, and the amount of suchprotection that is provided by other layers such as second electrode208, outer layer 212 may be omitted.

In industrial practice it may be difficult to control the azimuthorientation of a photoactive fiber structure (similar to 200, FIG. 2)in, for example, a cloth within which the fiber may be woven. In somecloth configurations, only 25% of a photoactive fiber's surface may beusefully exposed (compared to 50% in a conventional flat photovoltaiccell). A second electrode 208, comprised of, for example, ITO orPEDOT-PSS polymer, may be used. However, transparent electrodes, such asthose comprised of ITO and PEDOT-PSS, may be typically too resistive toconduct current along a length greater than about 1 cm. Accordingly, aauxiliary conductor 210 may be applied to and may be in electricalcontact with both organic layer 206 and second electrode 208. Theauxiliary conductor 210 may extract current over the entire length ofthe photoactive fiber structure 200. In an embodiment, the auxiliaryconductor 210 may be comprised of, for example, sliver, gold, copper, oraluminum. The auxiliary conductor 210 may be electrically coupled tosecond electrode 208, and may cover from about 5 percent to about 50percent of an external surface of second electrode 208. Additionally,while depicted in FIG. 2 as a solid wire, the auxiliary conductor may beany of at least a metallic wire, a metallized wire, a metallic ribbon, ametallized ribbon, and a metallic coating. The auxiliary conductor 210may be wound about the photoactive fiber structure 200, or may beapplied in a direction substantially parallel to the axis of supportelement 202. If wound, it is preferred that the duty cycle be low, suchthat the amount of surface covered by auxiliary conductor 210 isminimized, because auxiliary conductor 210 is not necessarilytransparent and it is desirable to minimize the amount of light that isblocked by the auxiliary conductor. The “duty cycle” is the axialdistance along a fiber in which auxiliary conductor 210 makes a completerevolution. A duty cycle of at least the circumference of the secondelectrode is preferred, to avoid blocking light from too much of theactive region. For most materials that may be desirable for use assecond electrode 208, and for most fiber dimensions, it is expected thatconduction in the axial direction, and not conduction around thecircumference of electrode 208, will be the issue addressed by auxiliaryconductor 210, such that there may not be a significant conductivitybenefit to a very small duty cycle. Where the solar fiber may beincorporated into a product such that the orientation of auxiliaryconductor 210 is not readily controlled, such as weaving into certaincloths where only a part of the fiber is expected to be exposed tolight, it may be preferred winding auxiliary conductor 210 with a dutycycle suffieciently low to avoid a situation where a fiber has anauxiliary conductor 210 is always oriented towards a light source so asto block a substantial fraction of the part of the fiber exposed tolight. Furthermore, in an embodiment, the auxiliary conductor 210 may bea braid of electrical conductors (not shown) surrounding secondelectrode 208, where the degree of occlusion from the braid ispreferably no more than about 50 percent. Although FIG. 3 illustrates anauxiliary conductor 210 that is separated from organic layer 206 bysecond electrode 208, such separation is not necessary and auxiliaryconductor 210 may contact organic layer 206. For example, auxiliaryconductor 210 may be fabricated prior to second electrode 208.

FIG. 3 shows a representation of a photoactive fiber structure 300similar to that of the photoactive fiber structure of FIG. 2, furtherincluding an exciton blocking layer 320, in accordance with anembodiment of the invention. The exciton blocking layer 320 may comprisea non-photoactive layer disposed between organic layer 206 and secondelectrode 208 such that non-photoactive exciton blocking layer 320 iselectrically coupled to each of organic layer 206 and second electrode208. Preferably, exciton blocking layer 320 is organic. For ease ofillustration, exciton blocking layer 320 is shown only in the magnifiedportion of FIG. 3. Other non-photoactive layers, preferably organic, maybe be included in a photoactive fiber structure, between first electrode204 and second electrode 208. For example, blocking layers, smoothinglayers, and any other layers that are known or may become known to theart may be incorporated into the fiber structure.

One method of making a photoactive fiber structure 200 in accordancewith the invention is coat a telecommunications fiber with ITO and thenuse vacuum thermal evaporation or dip-coating to deposit active organiclayer(s). A conductor (similar to 210, FIG. 2) may be deposited usingvacuum evaporation, after which the photoactive fiber may be testedusing common electrical probing techniques.

The dimensions of a practical photoactive fiber are subject to itsarchitecture, and both will be established simultaneously and somewhatiteratively. In general, when considering a generalized cylindricaldevice geometry as may be used in a flexible photoactive fiber woveninto fabric, the overall fiber thickness may range from about 10-100 μm,including the outer layer (similar to 212, FIG. 2), while the activeorganic layers (e.g., organic layer 206) may typically be only about 100nm thick.

The optical power absorbed by the active organic layers (e.g., organiclayer 206) is given approximately by:P _(opt) ≧Φ·d·L   (2)where, Φ, r₂, and L denote the optical flux, fiber radius at the anode,and uninterrupted fiber length, respectively. The resulting totalphotocurrent is given by: $\begin{matrix}{I_{PG} = \frac{P_{opt} \cdot \eta_{pwr}}{V_{OC} \cdot {FF}}} & (3)\end{matrix}$where, μ_(pwr), FF, and V_(oc) denote the photovoltaic cell powerefficiency, fill factor, and open-circuit voltage, respectively. (Thepower efficiency, η_(pwr) accounts for any additional absorption lossesto the incident solar flux in the structure.) The power produced in theload circuit is:P _(load) =V _(drop) ·I _(load)=(0.05·FF·V _(oc))·I_(PG)   (4)where, 5% voltage drop was allowed along the length of the fiber andI_(PG)=I_(load) during operation. At the same time, Ohm's law dictates:$\begin{matrix}{\frac{\left( {0.05 \cdot {FF} \cdot V_{OC}} \right)}{I_{load}} = \frac{\rho \cdot L}{A_{CS}}} & (5)\end{matrix}$where, ρ is the resistivity of the anode (e.g., second electrode 208and/or auxiliary conductor 210), while A_(cs)≈π·d·t is thecross-sectional area of the anode. Combining equations (2)-(5) obtains:$\begin{matrix}{t \geq \frac{\rho \cdot L^{2} \cdot \Phi \cdot \eta_{pwr}}{{.05} \cdot {FF}^{2} \cdot V_{OC}^{2}}} & (6)\end{matrix}$

If aluminum (p=5·10⁻⁸ Ω·m) were used as an inner conductor (similar to204, FIG. 2), and given η_(pwr)=3%, FF=0.5, Voc=0.5V, an estimate of theminimum thickness, in meters, of the inner conductor (similar to 204,FIG. 2) would be:t≧5·10⁻⁶ ·L ²   (7)where, L is also expressed in meters. Thus, a 5 μm thick coating of Alcan be used if the current is tapped out every 10 cm. This also sets thediameter of the conductor, viz.:π·d·t=π·d _(au) ²/4   (8)where, d_(au) is the diameter of the auxiliary conductor, such asauxiliary conductor 210, FIG. 2. Accordingly, from above, d_(au)=30 μm.

In one embodiment, the photoactive fiber structure 200, including theauxiliary conductor 210 may be wound together and then encapsulated by,for example, a 10 μm thick outer layer 212 to result in a slightlyoblong cross-section photoactive fiber structure that is about 110 μmacross its major diameter. This diameter may be suitable for typicaltextile processing equipment and incorporation into industrial andpersonal-use fabric.

It is believed that photoactive fiber structure in accordance with anembodiment of the invention may be fabricated at low-cost andincorporated into the high-speed manufacturing of textiles. One possiblecontinuous fabrication sequence may be to draw a metal or a metallizednylon core through a melt containing a blend of photosensitive polymer.The photosensitive polymer may dry and phase separate, resulting in abulk heterojunction structure surrounding the core. The core may then becoated with a conducting polymer (e.g., PEDOT). The conductor may beintroduced and wound together with the photogenerating core at a lowduty cycle, or may be linearly applied in a direction substantiallyparallel to the axis of the core of the photoactive fiber, to allowsufficient light absorption in the photoactive fiber. Finally, theentire photoactive fiber may be “finished” by encapsulation in atransparent plastic sheath or other protective outer layer to help toprotect it from mechanical (e.g., abrasive) and environmental damage.

Ultimately, the feasibility of installed solar panels depends on thecost of raw materials, fabrication, module assembly, transport, andon-site installation. While estimates of the final cost ofmass-manufactured photoactive fibers are only approximate, it isexpected to be less than that of silicon photovoltaic cells. The mass ofphotoactive polymer used in the photoactive fiber can be calculated fromthe dimensions obtained above. A 1 m long fiber will require ˜10⁻⁵ mg ofdry photoactive polymer, and a 1 m² swath of cloth woven from thephotoactive fiber will use ˜0.1 g of it. Chemicals such as C₆₀ arecurrently available in large quantities for <$30/gram (99% pure), andtheir price can be expected to drop in the near future. Nylon cloth isavailable to consumers at prices from $1 to $20 per m², depending on theweave, treatment, and strength, and at substantially lower cost tolarge-volume customers. A 3% efficient 1 m² photovoltaic cell cangenerate on average 30 Watts of electrical power. If the photoactivefiber cost is in the range of technical synthetic-based fabric price,the generated power can cost between ˜$0.1 and $0.8/Watt. A typicalsilicon-based solar cell has a $3-4/Watt installed cost. Furthermore,producing solar cells in the form of mechanically robust flexible fabriccan greatly reduce installation costs compared to heavy and bulkysilicon photovoltaic modules.

The nature of the polymers used to fabricate the photoactive fiber maypreferably satisfy several optical, electrical, mechanical, andrheological requirements. To maximize the efficiency of a solar cell,the absorption spectrum of the photo-generating layer should overlap thesolar radiation spectrum as much as possible. Conjugated polymerstypically have band gaps >2 eV, which omits a significant portion of theincident solar radiation. The structure and composition of the activepolymers can be modified to include the low-energy part of the solarspectrum using small-molecular-like side-branches and functional groupslike C₆₀. See, generally, Brabec, C. J., et al., Organic PhotovoltaicDevices Produced From Conjugated Polymer/Methanofullerene BulkHeterojunctions, Synthetic Metals, 2001, 121(1-3): p. 1517; Shaheen, S.E., et al., Low Band-Gap Polymeric Photovoltaic Devices, SyntheticMetals, 2001, 121: p. 1583.

However, structural modification of the polymer will also affect itsmelting temperature, Theological behavior, and crystalline order. Whilepolymer melt rheology is a well-studied topic, few studies exist dealingwith rheology of polymers used in photovoltaic cells; many have beensynthesized only in the last 5 years.

In addition to modifying the chemical structure of the photoactivepolymer, the optical absorption may be improved (“sensitized”) by dopinglow band-gap dye molecules into the host film. However, the excitonscreated on the dye molecules remain trapped due to their lower energyrelative to the surrounding polymer matrix. Engineering a three-phasemorphology on the nanometer scale, similar to that employed in a Gratzelcell may surmount this limitation. An amphiphilic dopant molecule may bemixed in with hydrophobic and hydrophilic polymers, such that uponannealing the amphiphilic dopant may create a third phase at theboundary between the two polymer phases. The net effect may be to absorband immediately dissociate a low-energy exciton at the ternaryinterface.

Charge and exciton hopping between neighboring chains also limit theoutput current of a photovoltaic cell. The operating hypothesis forbarrier coating design is that diffusion of chemical species (e.g. O₂and H₂O) into the photovoltaic cell causes decomposition of the photo-and electrically active compounds, accelerated by thermal and opticalstresses. While moisture diffusion coefficients can be low in somepolymeric materials, oxygen diffusion is more difficult to prevent.Metallic coatings are frequently used in some applications (e.g. foodpackaging, optical fiber coating, etc.), but they also block solar flux.Instead, transparent oxide (e.g. TiO₂, SiO₂, and Al2O3) coatings can beused for the solar fiber. The difficulty in using oxide thin films asdiffusion barriers in organic-based devices stems from a processing andapplication points of view. The deposition temperature for high-quality,dense oxides is typically high (>500° C.), while the decompositiontemperature of the organic materials is typically low (<500° C.). Theoxides are also brittle, with thermal expansion coefficients differentfrom polymers, so that cracks are easily formed during handling and use.Barrier coatings have been developed, where alternating polymer andsputtered metal-oxide inorganic thin films are employed. See, e.g.,Burrows, P. E., et al., Gas Permeation and Lifetime Tests onPolymer-Based Barrier Coatings, in SPIE Annual Meeting, 2000. Theinorganic layers act to block the diffusion of chemical species harmfulto the device, while the polymer interlayers act to cushion andmechanically decouple the oxide layers. Low-cost synthetic approaches,such as sol-gel synthesis of oxides may also be acceptable.

For OLED embodiments, organic layer 206 may comprise the organic layersof an organic light emitting device. Such layers are illustrated (in aplanar fashion) in FIG. 4, and described in further detail above andbelow. An auxiliary conductor may be used in an OLED embodiment toprovide current.

Hole transport layer 425 may include a material capable of transportingholes. Hole transport layer 430 may be intrinsic (undoped), or doped.Doping may be used to enhance conductivity. α-NPD and TPD are examplesof intrinsic hole transport layers. An example of a p-doped holetransport layer is m-MTDATA doped with F₄-TCNQ at a molar ratio of 50:1,as disclosed in United States Patent Application Publication No.2002-0071963 Al to Forrest et al., which is incorporated by reference inits entirety. Other hole transport layers may be used

Emissive layer 435 may include an organic material capable of emittinglight when a current is passed between anode 415 and cathode 460.Preferably, emissive layer 435 contains a phosphorescent emissivematerial, although fluorescent emissive materials may also be used.Phosphorescent materials are preferred because of the higher luminescentefficiencies associated with such materials. Emissive layer 435 may alsocomprise a host material capable of transporting electrons and/or holes,doped with an emissive material that may trap electrons, holes, and/orexcitons, such that excitons relax from the emissive material via aphotoemissive mechanism. Emissive layer 435 may comprise a singlematerial that combines transport and emissive properties. Whether theemissive material is a dopant or a major constituent, emissive layer 435may comprise other materials, such as dopants that tune the emission ofthe emissive material. Emissive layer 435 may include a plurality ofemissive materials capable of, in combination, emitting a desiredspectrum of light. Examples of phosphorescent emissive materials includeIr(Ppy)₃. Examples of fluorescent emissive materials include DCM andDMQA. Examples of host materials include Alq₃, CBP and mCP. Examples ofemissive and host materials are disclosed in U.S. Pat. No. 6,303,238 toThompson et al., which is incorporated by reference in its entirety.Emissive material may be included in emissive layer 435 in a number ofways. For example, an emissive small molecule may be incorporated into apolymer. This may be accomplished by several ways: by doping the smallmolecule into the polymer either as a separate and distinct molecularspecies; or by incorporating the small molecule into the backbone of thepolymer, so as to form a co-polymer; or by bonding the small molecule asa pendant group on the polymer. Other emissive layer materials andstructures may be used. For example, a small molecule emissive materialmay be present as the core of a dendrimer.

Many useful emissive materials include one or more ligands bound to ametal center. A ligand may be referred to as “photoactive” if itcontributes directly to the photoactive properties of an organometallicemissive material. A “photoactive” ligand may provide, in conjunctionwith a metal, the energy levels from which and to which an electronmoves when a photon is emitted. Other ligands may be referred to as“ancillary.” Ancillary ligands may modify the photoactive properties ofthe molecule, for example by shifting the energy levels of a photoactiveligand, but ancillary ligands do not directly provide the energy levelsinvolved in light emission. A ligand that is photoactive in one moleculemay be ancillary in another. These definitions of photoactive andancillary are intended as non-limiting theories. Note that the term“photoactive” as used herein generally means pertaining directly to theabsorption or emission of light. The specific meanings provided in thecontexts of an OLED as opposed to a photosensitive device are contextualapplications of the general definition.

Electron transport layer 440 may include a material capable oftransporting electrons. Electron transport layer 440 may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity. Alq₃ isan example of an intrinsic electron transport layer. An example of ann-doped electron transport layer is BPhen doped with Li at a molar ratioof 1:1, as disclosed in United States Patent Application Publication No.2002-0071963 Al to Forrest et al., which is incorporated by reference inits entirety. Other electron transport layers may be used.

The charge carrying component of the electron transport layer may beselected such that electrons can be efficiently injected from thecathode into the LUMO (Lowest Unoccupied Molecular Orbital) energy levelof the electron transport layer. The “charge carrying component” is thematerial responsible for the LUMO energy level that actually transportselectrons. This component may be the base material, or it may be adopant. The LUMO energy level of an organic material may be generallycharacterized by the electron affinity of that material and the relativeelectron injection efficiency of a cathode may be generallycharacterized in terms of the work function of the cathode material.This means that the preferred properties of an electron transport layerand the adjacent cathode may be specified in terms of the electronaffinity of the charge carrying component of the ETL and the workfunction of the cathode material. In particular, so as to achieve highelectron injection efficiency, the work function of the cathode materialis preferably not greater than the electron affinity of the chargecarrying component of the electron transport layer by more than about0.75 eV, more preferably, by not more than about 0.5 eV. Similarconsiderations apply to any layer into which electrons are beinginjected.

Blocking layers in an OLED may be used to reduce the number of chargecarriers (electrons or holes) and/or excitons that leave the emissivelayer. An electron blocking layer 430 may be disposed between emissivelayer 435 and the hole transport layer 425, to block electrons fromleaving emissive layer 435 in the direction of hole transport layer 425.Similarly, a hole blocking layer 440 may be disposed between emissivelayer 135 and electron transport layer 445, to block holes from leavingemissive layer 435 in the direction of electron transport layer 440.Blocking layers may also be used to block excitons from diffusing out ofthe emissive layer. The theory and use of blocking layers is describedin more detail in U.S. Pat. No. 6,097,147 and United States PatentApplication Publication No. 2002-0071963 A1 to Forrest et al., which areincorporated by reference in their entireties.

As used herein, and as would be understood by one skilled in the art,the term “blocking layer” means that the layer provides a barrier thatsignificantly inhibits transport of charge carriers and/or excitonsthrough the device, without suggesting that the layer necessarilycompletely blocks the charge carriers and/or excitons. The presence ofsuch a blocking layer in a device may result in substantially higherefficiencies as compared to a similar device lacking a blocking layer.Also, a blocking layer may be used to confine emission to a desiredregion of an OLED.

Generally, injection layers are comprised of a material that may improvethe injection of charge carriers from one layer, such as an electrode oran organic layer, into an adjacent organic layer. Injection layers mayalso perform a charge transport function. In device 400, hole injectionlayer 420 may be any layer that improves the injection of holes fromanode 415 into hole transport layer 425. CuPc is an example of amaterial that may be used as a hole injection layer from an ITO anode415, and other anodes. In device 400, electron injection layer 450 maybe any layer that improves the injection of electrons into electrontransport layer 445. LiF/Al is an example of a material that may be usedas an electron injection layer into an electron transport layer from anadjacent layer. Other materials or combinations of materials may be usedfor injection layers. Depending upon the configuration of a particulardevice, injection layers may be disposed at locations different thanthose shown in device 400. More examples of injection layers areprovided in U.S. patent application Ser. No. 09/931,948 to Lu et al.,which is incorporated by reference in its entirety. A hole injectionlayer may comprise a solution deposited material, such as a spin-coatedpolymer, e.g., PEDOT:PSS, or it may be a vapor deposited small moleculematerial, e.g., CuPc or MTDATA.

A hole injection layer (HIL) may planarize or wet the anode surface soas to provide efficient hole injection from the anode into the holeinjecting material. A hole injection layer may also have a chargecarrying component having HOMO (Highest Occupied Molecular Orbital)energy levels that favorably match up, as defined by theirherein-described relative ionization potential (IP) energies, with theadjacent anode layer on one side of the HIL and the hole transportinglayer on the opposite side of the HIL. The “charge carrying component”is the material responsible for the HOMO energy level that actuallytransports holes. This component may be the base material of the HIL, orit may be a dopant. Using a doped HIL allows the dopant to be selectedfor its electrical properties, and the host to be selected formorphological properties such as wetting, flexibility, toughness, etc.Preferred properties for the HIL material are such that holes can beefficiently injected from the anode into the HIL material. Inparticular, the charge carrying component of the HIL preferably has anIP not more than about 0.7 eV greater that the IP of the anode material.More preferably, the charge carrying component has an IP not more thanabout 0.5 eV greater than the anode material. Similar considerationsapply to any layer into which holes are being injected. HIL materialsare further distinguished from conventional hole transporting materialsthat are typically used in the hole transporting layer of an OLED inthat such HIL materials may have a hole conductivity that issubstantially less than the hole conductivity of conventional holetransporting materials. The thickness of the HIL of the presentinvention may be thick enough to help planarize or wet the surface ofthe anode layer. For example, an HIL thickness of as little as 10 nm maybe acceptable for a very smooth anode surface. However, since anodesurfaces tend to be very rough, a thickness for the HIL of up to 50 nmmay be desired in some cases.

A protective layer may be used to protect underlying layers duringsubsequent fabrication processes. For example, the processes used tofabricate metal or metal oxide top electrodes may damage organic layers,and a protective layer may be used to reduce or eliminate such damage.In device 400, protective layer 455 may reduce damage to underlyingorganic layers during the fabrication of cathode 460. Preferably, aprotective layer has a high carrier mobility for the type of carrierthat it transports (electrons in device 400), such that it does notsignificantly increase the operating voltage of device 400. CuPc, BCP,and various metal phthalocyanines are examples of materials that may beused in protective layers. Other materials or combinations of materialsmay be used. The thickness of protective layer 455 is preferably thickenough that there is little or no damage to underlying layers due tofabrication processes that occur after organic protective layer 460 isdeposited, yet not so thick as to significantly increase the operatingvoltage of device 400. Protective layer 455 may be doped to increase itsconductivity. For example, a CuPc or BCP protective layer 460 may bedoped with Li. A more detailed description of protective layers may befound in U.S. patent application Ser. No. 09/931,948 to Lu et al., whichis incorporated by reference in its entirety.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink-jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

The molecules disclosed herein may be substituted in a number ofdifferent ways without departing from the scope of the invention. Forexample, substituents may be added to a compound having three bidentateligands, such that after the substituents are added, one or more of thebidentate ligands are linked together to form, for example, atetradentate or hexadentate ligand. Other such linkages may be formed.It is believed that this type of linking may increase stability relativeto a similar compound without linking, due to what is generallyunderstood in the art as a “chelating effect.”

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18 degrees C. to 30 degrees C., andmore preferably at room temperature (20-25 degrees C.)

Although the present invention is described with respect to particularexamples and preferred embodiments, it is understood that the presentinvention is not limited to these examples and embodiments. The presentinvention as claimed may therefore include variations from theparticular examples and preferred embodiments described herein, as willbe apparent to one of skill in the art.

1. A structure, comprising: a conductive core including a firstelectrode; an organic layer surrounding the core and electricallyconnected to the first electrode; and a transparent second electrodesurrounding and electrically connected to the organic layer.
 2. Thestructure of claim 1, wherein the core includes a non-conductive supportelement and a conductive first electrode surrounding the non-conductivesupport element.
 3. The structure of claim 2, wherein the supportelement comprises a nylon fiber.
 4. The structure of claim 2, whereinthe support element comprises an optical fiber.
 5. The structure ofclaim 1, wherein the conductive core comprises a metal wire
 6. Thestructure of claim 1, further comprising an electrically conductiveauxiliary conductor electrically coupled to the second electrode.
 7. Thestructure of claim 6, wherein the auxiliary conductor has an axissubstantially parallel to an axis of the core.
 8. The structure of claim6, wherein the auxiliary conductor is wound around the second electrodewith a duty cycle of at least about the circumference of the secondelectrode.
 9. The structure of claim 6, wherein the auxiliary conductoris one of a metallic wire, a metallized wire, a metallic ribbon, ametallized ribbon, and a metallic coating.
 10. The structure of claim 6,wherein the auxiliary conductor is braid of electrical conductorssurrounding the second electrode.
 11. The structure of claim 1, whereinthe first electrode comprises a material selected from the groupconsisting of silver, gold, copper, and aluminum.
 12. The structure ofclaim 1, wherein the second electrode comprises a material selected fromthe group consisting of PEDOT and PSS.
 13. The structure of claim 1,wherein the first electrode, the organic layer, and the second electrodecomprise a photosensitive device, and the organic layer comprises aphotoactive region.
 14. The structure of claim 13, wherein the organiclayer further comprises a non-photoactive region.
 15. The structure ofclaim 14, wherein the non-photoactive region is an exciton blockinglayer.
 16. The structure of claim 13, wherein the photoactive regioncomprises a heterojunction between a pair of organic materials, the pairof organic materials being selected from the group consisting ofPCBM/MDMO-PPV, CuPc/C₆₀, and CuPc/PTCBI.
 17. The structure of claim 1,further comprising an outer layer surrounding the second electrode. 18.The structure of claim 1, wherein the first electrode, the organiclayer, and the second electrode comprise an organic light emittingdevice, and the organic layer comprises a light emitting layer.
 19. Thestructure of claim 18, wherein the organic layer further comprises anon-emissive layer.
 20. The structure of claim 19, wherein the organiclayer further comprises first and second blocking layers disposedadjacent to and in physical contact with the emissive layer.
 21. Afabric, comprising a plurality of fibers, each fiber further comprising:a conductive core including a first electrode; a first organic layersurrounding the core and electrically connected to the first electrode;and a transparent second electrode surrounding and electricallyconnected to the organic layer.
 20. A method, comprising: coating aconductive core including a first electrode with an organic layer;depositing a second electrode over the organic layer.
 21. The method ofclaim 20, further comprising: applying an electrically conductiveconductor over the second electrode.
 22. The method of claim 20, whereinthe first electrode, the organic layer, and the second electrodecomprise a photosensitive device, and the organic layer comprises aphotoactive region.
 23. The method of claim 20, wherein the firstelectrode, the organic layer, and the second electrode comprise anorganic light emitting device, and the organic layer comprises anemissive layer.
 24. The method of claim 20, wherein the conductive coreis coated with the organic layer by dip-coating.